Tip: Make sure the signal booster you buy works with your phone's wireless frequency. While a phone can operate on multiple frequencies, it only works on one frequency band at a time. Consider a dual-band signal booster. Fire up Femtocell: These mini cell towers target indoor users living in areas where even signal outdoors is mediocre. Unlike boosters, femtocells require a home broadband Internet connection, like a cable modem, which it converts into a cellular signal. Phone calls aren't routed over Wi-Fi (unless you're using T-Mobile's Wi-Fi calling alternative), but rather they use the same cellular technology your phone already uses, which is better on battery life. They also require GPS because each device is set to operate on a specific mobile network, as approved by your phone company. Only recently have carriers begun offering distressed users a free Femtocell. Otherwise, it costs between $100 to $300, plus a possible monthly fee. In the U.S., Sprint ( S) offers the Airave, Verizon ( VZ) has the Network Extender and AT&T ( T ) offer the Microcell femtocells. Here's a chart of international mobile carriers offering femtocells, as pieced together by the Small Cell Forum. Tip: Femtocells aim to improve voice calls and not necessarily data transmissions. The industry assumes users will stick to Wi-Fi to increase a phone's data speeds indoors. This article was written by an independent contributor, separate from TheStreet's regular news coverage.